Computing devices, such as smart phones and tablet computers, are becoming ubiquitous. It can be beneficial for these devices to have the ability to identify and/or authenticate a user. User identification can include determining which user is currently using the device. User authentication can include verifying the identity of the user. Providing user identification and authentication functionality can be challenging. For example, the components to provide this functionality can be expensive. Additionally, with respect to portable computing devices, the components can present a problem because they can take up significant space.